This invention relates to a camera with a built-in electronic flash device and an electronic flash device provided with an automatic emission control circuit which emits a flash light, receives reflected light having been reflected by an photographic object by a light receiving element, and stops the emission of the flash light when the reflected light reaches a specified amount.
It has been heretofore known an automatic control electronic flash device which emits a flash light, receives reflected light having been reflected by a photographic object by a light receiving element provided in an electronic flash circuit, and stops the emission of the flash light when the reflected light reaches a specified amount; it has been proposed to build such an automatic control electronic flash device in a lens-fitted film unit or a simple camera. According to this, without providing a complex flash-automatic stop mechanism which varies the aperture stop in accordance with the photographing distance, a proper exposure can be always obtained regardless of the variation of the photographing distance, because the amount of flash light varies in accordance with the photographing distance with the aperture stop kept constant.
In the case where such an automatic control electronic flash device as mentioned in the above is built in a lens-fitted film unit or a simple camera, automatic emission control can be made from the shortest distance to the longest distance. In the above, the shortest distance implies the shortest photographing distance determined by the limit of exposure and focusing, and the longest distance implies the longest photographing distance determined by the guide number at full emission of flash light and the predetermined constant aperture stop value. To practice an automatic emission control at a distance falling within the above-mentioned range implies theoretically that a flash light is emitted in such a manner as to reach a light quantity suitable corresponding to the guide number, that is, the product of the constant aperture stop value multiplied by the photographing distance.
However, practically it is difficult to control the light quantity in such a manner as to reach the theoretical amount of light emission; a dispersion of the amount of light emission is produced owing to a dispersion of electrical parts etc. In order to make the amount of light emission having such a dispersion come close to the theoretical amount of light emission, it has been necessary to use high-priced electrical parts having very little dispersion or to make an adjustment for each device using a variable resistor or the like. As the result of this, an electronic flash device provided with an automatic emission control circuit became of high price, which made it difficult to build it in a lens-fitted film unit or a simple camera to which low price is essential.
In view of the above-mentioned problem, the inventors, after having carried out various photographing tests using a color negative film, found out an emission control level without practical problem even if there is a dispersion to some extent. It is an object of this invention to propose a camera with a built-in electronic flash device and an electronic flash device provided with an automatic emission control circuit having such an emission control level.
Further, another object of this invention will be explained below.
It has been heretofore known an electronic flash device which emits flash light, receives reflected light having been reflected by a photographic object by a light receiving element provided in an electronic flash circuit, and stops the emission of the flash light by actuating a thyristor when the reflected light reaches a specified amount; it has been proposed to build such an electronic flash device in a lens-fitted film unit or a simple camera. According to this, without providing a complex flash-automatic stop mechanism which varies the aperture stop in accordance with the photographing distance, a proper exposure can be always obtained regardless of the variation of the photographing distance, because the amount of flash light varies in accordance with the photographing distance with the aperture stop kept constant.
A switching device composed of a thyristor or the like has a characteristic such that the performance varies in accordance with the variation of environmental temperature. Accordingly, if a switching device is used in an electronic flash device provided with an automatic emission control circuit, the emission control capability varies with temperature variation. Further, if the emission control capability is varied too much by the temperature dependence of the switching device, a proper exposure cannot be made for a film, which makes it meaningless to build an automatic emission control circuit in the flash device. For this reason, it is necessary to use a switching device having a temperature characteristic regulated in a certain range; however, heretofore it has not been known how to regulate the temperature characteristic of a switching device for an automatic emission control circuit.
This invention has been made in view of the above-mentioned problem; it is another object of this invention to propose an electronic flash device provided with an automatic emission control circuit having the temperature characteristic of the switching device regulated within a proper range.
On the other hand, the less becomes the variation of the emission control capacity owing to the temperature characteristic of the switching device composed of a thyristor or the like, the more desirable it is for the automatic emission control circuit.
This invention has been made in view of the above-mentioned problem; it is still another object of this invention to propose an electronic flash device provided with an automatic emission control circuit which is less susceptible to the influence of the temperature characteristic of the switching device.
Further, it was large the size of a switching device composed of a thyristor or the like for use in an electronic flash device provided with a conventional automatic emission control circuit, and its unit price also was high. For this reason, it has been difficult to build an electronic flash device provided with an automatic emission control circuit in a lens-fitted film unit or a simple camera which is of small size and of low price.
This invention has been made in view of the above-mentioned problem; it is still another object of the invention to propose an electronic flash device provided with an automatic emission control circuit having a small-sized and low-priced switching device.
The above-mentioned objects can be accomplished by any one of structures described below.
Structure 1: A camera with a built-in electronic flash device comprising a photographing lens, an aperture stop, a flash emitting portion, a light receiving element for receiving reflected light by a photographic object which has been emitted by the flash emitting portion, and a flash circuit for making the flash emitting portion emit light having an automatic emission control circuit which stops the emission of the flash emitting portion when the amount of the reflected light received by the light receiving element reaches a specified value, wherein with respect to the automatic emission control circuit, A min satisfies the following conditional expression for a theoretical exposure value A,
(Axe2x88x921)EVxe2x89xa6A minxe2x89xa6(A+0.5)EV,
where A min is a minimum exposure value for a recording medium on which a specified photographic object is recorded when the photographic object located at a distance falling within a range from a specified shortest distance to a distance determined by the guide number of the flash emitting portion at full emission and the aperture stop is photographed.
Structure 2: A camera with a built-in electronic flash device as set forth in structure 1, wherein A max and the aforesaid minimum exposure value A min satisfy the following conditional expression,
0.3 EVxe2x89xa6A maxxe2x88x92A min,
where A max is a maximum exposure value for a recording medium on which a specified photographic object is recorded when the photographic object located at a distance falling within a range from a specified shortest distance to a distance determined by the guide number of the flash emitting portion at full emission and the aforesaid aperture stop is photographed.
Structure 3: A camera with a built-in electronic flash device as set forth in structure 1, wherein A min satisfies the following conditional expression,
(Axe2x88x920.5)EVxe2x89xa6A minxe2x89xa6(A+0.5)EV.
Structure 4: A camera with a built-in electronic flash device as set forth in structure 1, wherein with respect to the automatic emission control circuit, A max satisfies the following conditional expression,
A maxxe2x89xa6(A+1.5)EV,
where A max is a maximum exposure value for a recording medium on which a specified photographic object is recorded when the photographic object located at a distance falling within a range from a specified shortest distance to a distance determined by the guide number of the flash emitting portion at full emission and the aperture stop is photographed.
Structure 5: A camera with a built-in electronic flash device as set forth in structure 1, wherein A max satisfies the following conditional expression,
A maxxe2x89xa6(A+1.2)EV.
Structure 6: A camera with a built-in electronic flash device as set forth in structure 1, wherein the aforesaid shortest distance is set at 1 m.
Structure 7: A camera with a built-in electronic flash device as set forth in structure 1, wherein the camera with a built-in electronic flash device is a lens fitted film unit.
Structure 8: A camera with a built-in electronic flash device as set forth in structure 1, wherein the aforesaid automatic emission control circuit has a switching device, and the automatic emission control circuit stops the emission of the aforesaid flash emitting portion by actuating the switching device when the amount of the reflected light received by the aforesaid light receiving element reaches a specified value.
Structure 9: A camera with a built-in electronic flash device as set forth in structure 8, wherein
D/C is from 1 to 1.4,
where C is the threshold gate voltage of the aforesaid switching device at the environmental temperature of 25xc2x0 C., and D is the threshold gate voltage of the switching device at the environmental temperature of 0xc2x0 C.
Structure 10: A camera with a built-in electronic flash device as set forth in structure 8, wherein the aforesaid switching device is such one that the threshold gate voltage varies in accordance with environmental temperature, and the aforesaid automatic emission control circuit has a temperature compensating element for varying the applied voltage to the gate of the switching device to such a direction that the threshold gate voltage of the switching device varies in accordance with environmental temperature.
Structure 11: A camera with a built-in electronic flash device as set forth in structure 8, wherein the current square time product of the aforesaid switching device is from 1 A2S to 32 A2S, the aforesaid flash circuit has a main capacitor, and the capacitance of the main capacitor is from 10 xcexcF to 120 xcexcF.
Structure 12: A camera with a built-in electronic flash device as set forth in structure 8, wherein the aforesaid switching device is a thyristor.
Structure 13: A camera with a built-in electronic flash device comprising a photographing lens, an aperture stop, a flash emitting portion, a light receiving element for receiving a reflected light by a photographic object which has been emitted by the flash emitting portion, and a flash circuit for making the flash emitting portion emit light having an automatic emission control circuit which stops the emission of the flash emitting portion when the amount of the reflected light received by the light receiving element reaches a specified value, wherein with respect to the automatic emission control circuit, A min and A max satisfy the following conditional expressions for a theoretical exposure value A,
(Axe2x88x921)EVxe2x89xa6A minxe2x89xa6(A+0.5)EV,
and
0.3 EVxe2x89xa6A maxxe2x88x92A min,
where A min and A max are a minimum exposure value and a maximum exposure value respectively for a recording medium on which a specified photographic object is recorded when the photographic object located at a distance falling within a range from a specified shortest distance to a distance determined by the guide number of the flash emitting portion at full emission and the aperture stop is photographed.
Structure 14: An electronic flash device comprising a flash emitting portion, and a flash circuit having an automatic emission control circuit for making the flash emitting portion emit light, wherein the automatic emission control circuit stops the emission of the flash emitting portion when the amount of the reflected light by a photographic object which has been emitted by the flash emitting portion reaches a specified value, and with respect to the automatic emission control circuit, A min satisfies the following conditional expression for a theoretical exposure value A,
xe2x80x83(Axe2x88x921)EVxe2x89xa6A minxe2x89xa6(A+0.5)EV,
where A min is a minimum exposure value for a recording medium on which a specified photographic object is recorded when the photographic object located at a distance falling within a range from a specified shortest distance to a distance determined by the guide number of the flash emitting portion at full emission and the aperture stop is photographed.
Structure 15: An electronic flash device comprising a flash emitting portion, and a flash circuit having an automatic emission control circuit for making the flash emitting portion emit light, wherein the automatic emission control circuit stops the emission of the flash emitting portion when the amount of the reflected light by a photographic object which has been emitted by the flash emitting portion reaches a specified value, and with respect to the automatic emission control circuit, A min and A max satisfy the following conditional expressions for a theoretical exposure value A,
(Axe2x88x921)EVxe2x89xa6A minxe2x89xa6(A+0.5)EV,
and
0.3 EVxe2x89xa6A maxxe2x88x92A min,
where A min and A max are a minimum exposure value and a maximum exposure value respectively for a recording medium on which a specified photographic object is recorded when the photographic object located at a distance falling within a range from a specified shortest distance to a distance determined by the guide number of the flash emitting portion at full emission and the aperture stop is photographed.
Further, desirable structures are such ones as described below.
Structure 16: A camera with a built-in electronic flash device provided with an automatic emission control circuit which emits a flash light, receives the reflected light having been reflected by an photographic object by a light receiving element, and stops the emission of the flash light when the amount of the reflected light reaches a specified value, wherein the automatic emission control circuit carries out the emission control in a manner such that A min satisfies the following conditional expression for a theoretical exposure value A,
(Axe2x88x921)EVxe2x89xa6A minxe2x89xa6(A+0.5)EV,
where A min is a minimum exposure value for a recording medium on which a specified photographic object is recorded when the photographic object located at a distance falling within a range from a specified shortest distance to a distance determined by the guide number at full emission and the aperture stop is photographed.
Structure 17: A camera with a built-in electronic flash device as set forth in structure 16, wherein the automatic emission control circuit carries out the emission control in a manner such that the aforesaid minimum exposure value A min satisfies the following conditional expression for a theoretical exposure value A,
(Axe2x88x920.5)EVxe2x89xa6A minxe2x89xa6(A+0.5)EV.
Structure 18: A camera with a built-in electronic flash device as set forth in structure 16 or structure 17, wherein the automatic emission control circuit carries out the emission control in a manner such that A max satisfies the following conditional expression for a theoretical exposure value A,
A maxxe2x89xa6(A+1.5)EV,
where A max is a maximum exposure value for a recording medium on which a specified photographic object is recorded when the photographic object located at a distance falling within a range from a specified shortest distance to a distance determined by the guide number at full emission and the aperture stop is photographed.
Structure 19: A camera with a built-in electronic flash device as set forth in structure 18, wherein the automatic emission control circuit carries out the emission control in a manner such that the aforesaid maximum exposure value A max satisfies the following conditional expression for a theoretical exposure value A,
A maxxe2x89xa6(A+1.2)EV.
Structure 20: A camera with a built-in electronic flash device as set forth in any one of structures 16 to 19, wherein the aforesaid shortest distance is 1 m.
Structure 21: A camera with a built-in electronic flash device as set forth in any one of structures 16 to 20, wherein the aforesaid camera with a built-in electronic flash device is a lens-fitted film unit.
Structure 22: A camera with a built-in electronic flash device provided with an automatic emission control circuit which emits a flash light, receives the reflected light having been reflected by an photographic object by a light receiving element, and stops the emission of the flash light when the amount of the reflected light reaches a specified value, wherein the automatic emission control circuit carries out the emission control in a manner such that A min satisfies the following conditional expression for a theoretical exposure value A,
(Axe2x88x921)EVxe2x89xa6A minxe2x89xa6(A+0.5)EV,
where A min is a minimum exposure value for a recording medium on which a specified photographic object is recorded when the photographic object located at a distance falling within a range from a specified shortest distance of the camera with a built-in electronic flash device to a distance determined by the guide number at full emission and the aperture stop of it is photographed.
Structure 23: An electronic flash device provided with an automatic emission control circuit which emits a flash light, receives the reflected light having been reflected by an photographic object by a light receiving element, and stops the emission of the flash light by actuating a switching device when the amount of the reflected light reaches a specified value, wherein
B/A is from 1 to 1.4,
where A is the threshold gate voltage of the switching device at the environmental temperature of 25xc2x0 C., and B is the threshold gate voltage of the switching device at the environmental temperature of 0xc2x0 C.
Structure 24: An electronic flash device provided with an automatic emission control circuit which emits a flash light, receives the reflected light having been reflected by an photographic object by a light receiving element, and stops the emission of the flash light by actuating a switching device when the amount of the reflected light reaches a specified value, wherein the switching device is such one that the threshold gate voltage varies in accordance with environmental temperature, and a temperature compensating element for varying the voltage applied to the gate of the switching device, to such a direction that the threshold gate voltage of the switching device varies in accordance with environmental temperature, is used for at least one of the electrical elements which makes up the circuit for controlling the gate of the switching device in the automatic emission control circuit.
Structure 25: An electronic flash device provided with an automatic emission control circuit which emits a flash light, receives the reflected light having been reflected by an photographic object by a light receiving element, and stops the emission of the flash light by actuating a switching device when the amount of the reflected light reaches a specified value, wherein a switching device having a current square time product from 1 A2S to 32 A2S is used for the switching device, and a capacitor having a capacitance falling within a range from 10 xcexcF to 120 xcexcF is used for the main capacitor of the electronic flash device.
Structure 26: An electronic flash device as set forth in any one of structures 23 to 25, wherein the aforesaid switching device is a thyristor.
Structure 27: A camera having built in the aforesaid electronic flash device set forth in any one of structures 23 to 26.
Structure 28: A lens-fitted film unit having built in the aforesaid electronic flash device set forth in any one of structures 23 to 26.